Recent advances in personal communications have enabled people to employ a variety of communication devices (e.g. one or more wireline telephones such as an office phone and a home phone, one or more wireless telephones, one or more desktop PCs equipped with a connection to the Internet such as through a modem connected to a plain old telephone service (POTS) line, ISDN line, T1 line, T3 line, digital subscriber line (DSL) line, or cable, one or more portable PCs similarly equipped, a FAX machine, a pager, a personal data assistant (PDA), etc.). Further, the capabilities of individual devices continue to expand (e.g. modern voice telephones are often equipped with displays, etc.). Many of these devices provide access to one or more networks, such as the Internet, PSTN, etc.
There is currently a thrust to develop a method of delivering a variety of services independent of the access network employed. Many of the services involve mobility (e.g., the ability to access location-specific travel services such as local restaurant listings, guides, and reservations while on the road).
When considering the delivery of services to mobile users, it is useful to distinguish between two types of mobility: terminal mobility (i.e., the ability for an individual to roam with a particular device across some geographic location without interrupting service) and personal mobility (i.e., the ability for an individual to move from one device to another, while seamlessly preserving access to a common set of services). In some cases, it is desirable to provide the ability to migrate a service from one device to another without interrupting the service.
Terminal Mobility
Considerable effort has been devoted to supporting terminal mobility. Wireless LANs (e.g., IEEE 802.11) and wireless cellular networks typically implement terminal mobility at layer 2 (relative to Internet Protocol (IP)). In addition, Mobile IP (RFC 2002) is a layer-3 solution that has been developed for generalized IP networks.
One of the challenges in providing terminal mobility is the ability to route packets efficiently in the network. Essentially, once a node is associated with a given IP address, packets destined to that node may only be routed to the topological location corresponding to the address, which may be distant from the node's physical location. Thus, if an individual from Europe visits North America, packets routed to the IP address corresponding to the individual's device will be routed through Europe even if communicating with local services. As such, when roaming across wide geographic areas (e.g., country to country), it may be preferable to modify a node's IP address, even at the cost of losing existing connections.
Personal Mobility
Traditionally, user services have been associated with specific access networks which in turn have been associated with specific devices (PCs may send messages only to other PCs over the Internet, telephones may send voice messages only to other telephones over the public switched telephone network (PSTN), etc.).
FIG. 1 generally depicts the conventional situation. A user's receipt of information from a service or of messages from another user has traditionally depended on a user's presence at a particular telephone set, a particular email address, etc. A barrier to achieving widespread personal mobility has been the lack of unification among access networks.
Instant messaging services are coming into widespread use. In an instant messaging service, a user may be reached only when on line in a particular access network (e.g., when logged on to an Internet service provider (ISP) under a login name that is registered with the instant messaging service, etc.). If a user is reachable by some other means (wireline phone, cell phone, pager, PDA, FAX, etc.), the present instant messaging services have no way to determine that the user is available and thus list the user as unreachable or logged off.
In other forms of user-to-user communication (e.g. telephone communications), a caller is currently unable to reach a called party who is unreachable at a telephone number known to the caller. For example, a potential called party staying in a hotel is reachable through the hotel's telephone number, but potential callers may not know that the called party is away from home. Although they might know the called party's home phone number and might call it, they would not succeed in speaking to the called party.
Thus, in conventional systems, end-user services are associated with specific access networks, which in turn are associated with specific devices having specific addressing (specific telephone numbers, specific email addresses, etc.).